Waxy corn starch: a potent cofiller in pellets produced by extrusion-spheronization

Immediate release of poorly soluble drugs from starch-based pellets prepared via extrusion/spheronisation

The aim of this study was to evaluate modified starch (high-amylose, crystalline and resistant starch) as the main excipient for immediate-release pellets containing poorly soluble drugs (hydrochlorothiazide and piroxicam) and prepared via extrusion/spheronisation. The bioavailability of pellets (containing 50 mg hydrochlorothiazide) was determined after oral administration to 6 dogs. A 2(4)-factorial design with central point was used to evaluate the influence of hydrochlorothiazide (10% and 50%, w/w), HPMC (binder, 4% and 7%, w/w), sorbitol (0% and 10%, w/w) and water (granulation liquid, low and high level) on pellet yield, size (Feret mean diameter) and sphericity (aspect ratio and two-dimensional shape factor, eR). Optimal granulation liquid content depended on drug and sorbitol level in the formulation. All factors except sorbitol content, as well as the interactions between drug concentration and binder level and between drug and water level, were significant (P<0.05) for pellet yield, while a significant curvature (P<0.05) suggested non-linearity of the response plots. The model was not significant for pellet shape, while hydrochlorothiazide and water level as well as their interaction were significant (P<0.05) for pellet size. Pellet friability, disintegration, residual water content and in-vitro drug release were determined. Pellets containing 2.5% (w/w) piroxicam were also evaluated. For both model drugs, pellets with a high yield (>90%), acceptable sphericity (AR<1.2) and low friability (<0.01%) were obtained. Due to pellet disintegration, fast dissolution of both hydrochlorothiazide and piroxicam was achieved: >80% drug released in 30 min. The bioavailability (AUC0-->24 h, Cmax and tmax) of hydrochlorothiazide pellets in dogs was not significantly different from fast-disintegrating immediate-release hydrochlorothiazide tablets (P>0.05).

Use of κ-carrageenan as alternative pelletisation aid to microcrystalline cellulose in extrusion/spheronisation. I. Influence of type and fraction of filler

Microcrystalline cellulose (MCC) is commonly used as an excipient in extrusion/spheronisation process. However, MCC has several disadvantages as lack of disintegration and drug adsorption. Therefore, kappa-carrageenan was investigated to substitute MCC in pelletising processes. Formulations with 20% of pelletisation aid (kappa-carrageenan or MCC) and acetaminophen as a model drug have been produced. Different fillers (lactose, mannitol, maize starch and dicalciumphosphate dihydrate) at fractions of 0, 20, 40 and 80% were evaluated and the properties of the resulted pellets were determined (e.g. yield, aspect ratio, mean Feret diameter, 10% interval fraction, tensile strength and release profile). kappa-Carrageenan has proven to be a suitable substitute as pellets with sufficient quality were produced. The pellet batches of different formulations were characterised by high yield, spherical pellet shape and narrow pellet size distribution. The distinguished behaviour between kappa-carrageenan and MCC pellets was the lower tensile strength and the faster release of kappa-carrageenan pellets. For the various types and fractions of fillers only minor effects to the pelletisation process and pellet properties were noticed. From the practical view these effects are neglectable indicating a robust formulation and process.

Starch–dextrin mixtures as base excipients for extrusion–spheronization pellets

Extrusion-spheronization pellets are generally produced with microcrystalline cellulose (MCC) as the principal excipient, giving rise to particles of very high quality. A number of alternative excipients have been proposed and evaluated, mostly other cellulose derivatives (e.g. different grades of Avicel), or mixtures of MCCs and other excipients. In the present study, we evaluated the possible use of starch+agglutinant mixtures as principal excipients for extrusion-spheronization pellets, with the aim of producing pellets with more suitable properties for certain types of release. We first characterized the different excipients in terms of morphometry and basic physical properties. Subsequently, torque-rheometry was used to characterize the rheology of wetted masses of the different excipients and excipient mixtures, with the aim of determining optimal amount of wetting agent (water). We also evaluated the water absorption and water retention capacities of each excipient. In view of the results obtained, we produced pellets with the different starch+agglutinant mixtures (but without drug), and used image analysis to characterize pellet morphology. Our results show that some of the mixtures-notably starch (corn starch or wheat starch)+20% white dextrin-gave high-quality pellets with good size and shape distributions. In addition, the properties of the different materials tested suggest that it may be possible to obtain pellets with very different properties.

Disintegrating pellets from a water-insoluble pectin derivative produced by extrusion/spheronisation

Pectinic acid (PA) and microcrystalline cellulose (MCC) as extrusion aiding excipients have been compared. Three different drugs were selected as models: Riboflavin with a very low water solubility, paracetamol and theophylline as drugs with high water-solubility. The drug load was varied from 1 to 80% wt. The low-soluble pectin derivative, PA (degree of methoxylation <10%) was found to be well suited as an extrusion aiding excipient in pellet preparation by extrusion/spheronisation. The substance has a high drug loading capacity and produces disintegrating pellets that are well suited for fast delivery of drugs with a low water-solubility. The pellets are also mechanically stable. Compared to MCC, PA was found to require less water for pellet formation and was more sensitive against changes in the water content. In order to achieve optimal shape of the pellets, spheronisation was carried out at 45 degrees C. PA is more sensitive to type and amount of drug and is, consequently, not as universally applicable as the conventionally used microcrystalline cellulose. The great advantage of pectinic acid is, however, the disintegrating properties of the pellets after only a short time of exposure to liquid.

Pectinic acid, a novel excipient for production of pellets by extrusion/spheronisation: preliminary studies

A very low soluble pectin-derivative (pectinic acid, degree of methoxylation 4%) was found to be well suited as an excipient for pelletisation by extrusion/spheronisation. Formulations containing pectinic acid and lactose in the following ratios were evaluated: 99/1, 80/20, 50/50 and 20/80. The capacity as an extrusion aid was found to be high; even formulations containing only 20% pectinic acid resulted in nearly spherical pellets. All pectinic acid pellets were mechanically stable, had an aspect ratio of approximately 1.15-1.20 and released 30-60% of a low solubility model drug within 15 min both in simulated gastric acid (0.1M HCl) and intestinal fluid (phosphate buffer pH 6.8).

Diffusion of a freely water-soluble drug in aqueous enteric-coated pellets

The effects of filler used in the pellet cores (ie, waxy cornstarch or lactose) and the enteric film coat thickness on the diffusion and dissolution of a freely soluble drug were studied. Two kinds of pellet cores containing riboflavin sodium phosphate as a model drug, microcrystalline cellulose (MCC) as a basic filler, and waxy cornstarch or lactose as a cofiller were film coated (theoretically weight increase 20% or 30%) with an aqueous dispersion of cellulose acetate phthalate (CAP). The diffusion of riboflavin sodium phosphate in aqueous enteric-coated pellets was investigated using noninvasive confocal laser scanning microscopy (CLSM). The in vitro release tests were performed using a USP apparatus I (basket method). Diffusion of drug from the core to the film coat was found to be greater with lactose-containing pellets than with waxy cornstarch-containing pellets. The dissolution test showed that 30% enteric-coated waxy cornstarch pellets had a good acidic resistance in 0.1 N HCl solution for at least 1 hour, while the other enteric pellet formulations failed the test. The waxy cornstarch-containing enteric pellets dissolved at SIF in less than 10 minutes. Confocal images of film-coated pellets showed that waxy cornstarch-containing pellets had less drug dissolved than respective lactose-containing pellets. The observations were further confirmed by measurement of fluorescence intensity of riboflavin sodium phosphate in the film coat. The dissolution test was consistent with the confocal microscopy results. In conclusion, waxy cornstarch as a cofiller in the pellet cores minimizes premature drug diffusion from the core into the film coat layer.

Investigation on the co-extrudability and spheronization properties of wet masses

In the present work, preliminary results of co-extrusion and spheronization of wet masses are reported. A ram co-extruder, manufactured in-house, was designed with two concentric single dies mounted on two concentric and independent chambers. This equipment has allowed the production of three types of extrudates (rod or solid extrudates, tubular or hollow extrudates and co-extrudates). Different wet mixtures of microcrystalline cellulose, lactose, a non-soluble in water dye and water were produced and used to feed the chambers of the ram co-extruder. Extrusions of the wet masses were carried out at different speeds of the ram (25-400 mm/min). The extrudates were evaluated according to surface characteristics (by visual inspection), force of extrusion and duration of steady-state (after recording the force applied to the ram and its displacement). Simultaneously, for each process of extrusion it was possible to assess the angles of convergence to the bottom of the chambers for both the external and internal chambers. These angles reflected the high complexity of the extrusion occurring on the external chamber in consequence of its annular geometry, in which the bisecting-line was not parallel to the axis of the extruder, by opposition to the converging angle in the internal chamber, where the bisecting-line was perfectly aligned to the axis of the extruder. Variations in the amount of water in the formulations and the speed of extrusion affected both the production and the quality of the extrudates and their ability to provide pellets. The rod extrudates were the easiest to produce and the relationships between the formulations, the processing conditions and the properties of the extrudates were immediately apparent. On the other hand, co-extrudates were more complex to characterise, although identical relationships between formulations, processing conditions and the properties of the co-extrudates were observed as for the rod extrudates. Different batches of extrudates (rod, tubular and co-extrudates) were spheronized to a maximum spheronization time of 10 min at 1000 rpm. The pellets were characterized with respect to size, size distribution, sphericity and density. Results have shown that for a larger diameter of the co-extrudates, the pellets produced were bigger ( approximately 3.38 mm) than the pellets produced from rod extrudates (1.22 mm). For longer times of spheronization, the aspect ratio and the density increased for both pellets produced from rod (0.95 and 1.46 g/cm(3)) and co-extrudates (0.90 and 1.47 g/cm(3)). The study has shown the potential of this new technology in providing a product with advantages over the traditional spheres produced by extrusion and spheronization.